Developmental ethanol exposure, involving postnatal days 4-6 (PN4-6) in rats, is a model of human exposure during the early third trimester and results in loss of Purkinje neurons of the cerebellum and functional deficits in motor skills and eye blink conditioning. Similar impairments are seen in human FASD. Climbing fibers from the inferior olive synapse on Purkinje cells and are an integral component for proper functioning. Few studies involving ethanol exposure have focused on the role of climbing fibers. We hypothesize that ethanol exposure in the early postnatal (developmental) stage negatively impacts the surviving neuronal components of the cerebellum by altering synaptic connections of the Purkinje cells to climbing fibers, independent of neuronal loss. We also theorize that ethanol-induced alterations in specific classes of glutamate receptors are mechanistically involved in these changes. We will utilize confocal microscopy to examine the 3-D morphology of these neuronal structures and the extent of ethanol-induced alterations, as they develop and mature. We propose the following Specific Aims: (1) Establish that climbing fibers are altered following postnatal ethanol exposure independent of Purkinje neuron loss. We will use rats treated with ethanol on PN4, PN4 6, and PN7 9. Purkinje neurons are vulnerable to ethanol exposure only during the PN4-6 window. (2) Evaluate the morphological development of Purkinje cells that survive postnatal ethanol exposure. We will characterize the morphological development of the soma and the dendritic tree of the surviving Purkinje cells in groups of rats receiving varying developmental exposures to ethanol compared to a control group. This in-depth analysis will provide the first such data for these surviving Purkinje neurons. (3) Determine whether the glutamate receptor subtypes, AMPA and mGluR, are causal mechanisms of ethanol-induced alterations of climbing fiber development. We will explore the mechanistic link between glutamate receptors and climbing fiber developmental connections by administering glutamate receptor blockers with and without concurrent ethanol exposure. We believe that a significant component of ethanol's actions is mediated by its blockage of these receptors during critical developmental periods. Our focus is on the status and continued development of the cerebellar structures that have survived the binge-like ethanol damage delivered at a time known to cause significant neuronal death. The ultimate goal of this work is then to derive from this knowledge a means or method for the maximum utilization of these remaining structures to provide the best outcome for the individual. Since no therapeutic intervention will replace the lost Purkinje cells, an understanding of the characteristics and nature of alterations in the intricate connections between climbing fibers and the surviving Purkinje neurons holds the promise of ameliorative treatments for children suffering from FASD.